1. Field of the Invention
The present invention relates generally to vacuum pumps and siphons, and more specifically to a hydraulic vacuum pump that uses a centrifugal pump in a new way to evacuate gases along with liquids, for priming siphons and for other uses where gases must be removed while mixed with liquids at subatmospheric pressure.
2. Description of Related Art
A siphon is a leakproof solid channel, shaped and positioned to carry liquid from a source up and over an elevated point and down to an outlet at a lower level. A siphon must have at least its upper (source) end submerged to allow atmospheric pressure to hold it full of liquid after it has been primed (filled), so that flow is powered by gravity. A siphon's elevation is the vertical rise from the liquid-surface of the source to the crown (highest part) of the siphon. Pressure within the elevated parts (every part between the source-surface and the crown) of a working siphon is always subatmospheric. The maximum elevation of liquid in a siphon depends on the specific gravity (sg) of the liquid and atmospheric pressure. Water at 1.0 sg can be elevated in a siphon to no higher than about 34 feet at sea level.
It should be noted that a fully operating siphon is very energy efficient. It moves liquid at the rate of flow the aforementioned factors permit, using only gravity for motive power and atmospheric pressure to hold liquid. But reliability of siphons needs improvement. Accidental starting or stopping of a siphon is often inconvenient, or costly, or dangerous.
Siphons are used in systems for flood control in rivers and reservoirs, chemical processes, desalination, power generation, motor vehicles, manufacturing, medicine, brewing, farming, livestock care, hatcheries, zoos, aquariums and many other uses.
Siphons can be built from many different man-made materials including reinforced concrete, pipes and fittings of metal or plastic, flexible tubing, and others. Modem materials make far better siphons than were available to ancient builders.
Atmospheric pressure of 14.7 pounds per square inch at sea level, is the weight of air pressing down on the earth's surface, and is the force that holds liquid in a siphon. Subatmospheric pressure, also called a vacuum, is in the elevated parts of working siphons.
Subatmospheric pressure in the elevated parts of a liquid-filled siphon, allows any leak to admit air. The lower pressure also causes gases that are dissolved in the liquid to effervesce. Thus, whenever enough air or other gases gradually enter the highest part or crown of a siphon to drop the liquid level below the crown, flow through the siphon is reduced. When the level drops below the bend or crest of the siphon, the flow stops entirely. And whenever air can enter freely, from an unsubmerged end or an unusually large break or leak in an elevated part, the siphon empties all liquid as fast as it can flow out. Freely admitting air to stop siphon flow can be done by installing a "vacuum breaker" valve at the crown. Blocking the siphon channel with a shutoff valve or end-cap will also stop flow, as will frozen liquid or clogged foreign matter. Most commonly the liquid moved through a siphon is unfrozen water, but many other free-flowing liquids can be siphoned. Most commonly the gas to be removed from a siphon is air, but any other gas that behaves like air could be there.
Before a siphon can efficiently start to carry water or any other liquid, all of the air or any other gas inside the siphon must be replaced by liquid. This process is called priming, filling or starting the siphon.
There are several well-known ways to start a siphon:
Inversion siphon-priming, well known to brewers, aquarium keepers and others, may be the most ancient method of siphon-starting still commonly used. A small siphon is inverted, filled by either immersion or pouring, and outflow is blocked until it is placed into a working siphon position.
The same human lung-power that makes a soda-straw work, is another ancient method often used to start small siphons.
Self-priming siphons have a low elevation so that siphoning begins when a rise in water level causes liquid to enter from the upper end, enough to cause continuous flow. The most common man-made self-priming siphons are rather large, typically made of reinforced concrete, with diameter, elevation and length measured in meters, most often used for controlling water levels in reservoirs. Other examples of self-priming siphons on a comparatively miniature scale, include U.S. Pat. Nos. 5,738,137; 4,846,206; and 4,124,035. The latter one is so small that capillary action affects its performance.
Induced-flow can start siphons that have a size or shape that restricts air-inlet from the lower end. Liquid is caused to flow through from the source end of the siphon, by any one of several different methods, until unassisted gravity-power can sustain continuous flow. The oldest known method of this kind was invented in the first century AD by Hero of Alexandria. The Internet in May, 1998, displayed two similar methods. One, under Siphons, was Starting a Python Siphon (for aquariums) by George Booth; and the other, under Siphons & Tubing, Phil's Psyphon Starter by brewguys.
Pumping or pouring full to the brim of an opened siphon-crown, will effectively prime a siphon in working position, provided that its lower ends are blocked shut. The crown-opening is then closed airtight before unblocking the lower ends; then flow can begin. This method of siphon-filling was introduced for an aquarium fish-bridge in U.S. Pat. No. 5,067,439.
Vacuum siphon-priming can fill any size siphon that is in working condition, either before startup or during operation, without moving the siphon itself. Air is extracted from the crown of the siphon, which allows atmospheric pressure to force liquid up into the evacuated space.
Other siphon-starters can only be used before the siphon begins to operate. Air in a working siphon inevitably rises to the top. If siphon-starting is limited to one of those methods and air in the siphon stops its flow, the startup process must usually be repeated after correcting, if possible, whatever problem allowed the air to get in.
The simplest form of vacuum-pump air-extraction for small siphons is a hand-operated bellows or squeeze-bulb equipped with one-way valves. Examples of this method of siphon-priming can be seen in U.S. Pat. Nos. 5,230,298; 3,670,758; and 192,595.
Many kinds of power-driven vacuum machines are well known. They include household vacuum cleaners, the inlet of an air pump or air compressor, industrial vacuum pumps that rapidly exhaust high volumes of air, sophisticated scientific machines that attain a near-perfect vacuum, and others. All of these are made for handling air or other gases alone, not mixed with liquids. Most air pumps and vacuum pumps would be damaged if liquid entered the pump itself. A method of either separating liquids from gases ahead of the pump inlet, or stopping the pump before liquid can enter, is commonly found where such machines may encounter liquids. With protection from liquid entry, vacuum machines designed to quickly move high volumes of air can be a very efficient way to exhaust air from a siphon, within limits of how much low pressure it can produce.
An example of vacuum-priming in a large-scale siphon, as described in a reference volume, was operated in a desalination plant on the island of Malta in 1975. A siphon 200 meters long, 4 meters in elevation and 0.8 meters diameter carried sea water to the plant. It was primed by a vacuum pump in about two hours. The vacuum pump was then operated continuously to extract entrained air.
Also well-known, but not found applicable to siphon-priming, is the subatmospheric pressure (vacuum) available at the inlet of any liquid-handling pump, whether centrifugal or positive-displacement. Measurement of the low pressure of such pump-inlets is often expressed in terms of "suction lift", which is the vertical distance that atmospheric pressure will force water upward to the pump inlet, minus losses due to flow-friction in the line. A mechanic's reference book typically states a limit of "practical suction lift" on positive-acting pumps as about 22 feet, and on centrifugal pumps about 15 feet. However, in order to obtain even that much "lift", a liquid handling pump must he "pre-primed"; that is, it must already be liquid-filled, or have liquid flowing through.
A dry centrifugal pump has no suction lift at all, and a dry positive-displacement pump would need very unusual seals against air leaks before it could produce enough suction lift to prime a siphon of very low elevation. Furthermore, positive displacement pumps often have difficulties attempting to handle air/water (gas/liquid) mixtures.
The venturi effect, based on Bernoulli's theorem which explains how pressure drops as speed increases in fluid flow, is another prior art way to vacuum-prime a siphon. Typically, the outflow of a liquid pump is passed through a venturi device to produce vacuum. Efficiency is low, but venturi-produced vacuum can prime a low-elevation siphon. Examples of venturi siphon-priming can be found in U.S. Pat. Nos. 4,036,756; 4,579,139; and 4,951,699.
The first fish-bridge siphon that interconnected two aquariums appeared in U.S. Pat. No. 192,595. Subsequently, fish bridge siphon variations are found in U.S. Pat. Nos. 1,576,462; 3,903,844; 5,067,439; and 5,230,298. More fish-display siphons for aquariums with very complex designs can be found in U.S. Pat. Nos. 5,282,438 and 5,605,115.
The inventor's U.S. Pat. No. 3,903,844 included circulation of aerated and filtered water in a double-tank fish-bridge siphon. A smaller siphon was built into the back edge of the fish-bridge. A small opening at the crown of the smaller siphon interconnected the two siphons. Water flowed slowly through the smaller siphon to the inlet of an air-bubble pump in one tank, and returned to the other tank through the larger siphon. The interconnection assured that neither siphon could carry water if the other stopped flowing. This effectively prevented tank overflow.
A large scale siphon design for tidal water power to produce electricity is found in U.S. Pat. No. 4,288,985. A giant siphon would carry the rise and fall of ocean tides through a hydro turbine generator. However, one of its major design shortcomings is the omission of a way to prime the huge siphon or to maintain prime, essential for successful operation.
In all of the prior art methods of siphon-priming there are many needs for improvement:
(a) Priming by inversion is undesirable wherever spills could be damaging or dangerous; PA1 (b) Lungpower siphon-filling, besides other limitations, is often unsanitary and hazardous; PA1 (c) Self-priming siphons work only for low-elevations, with limited control; PA1 (d) Induced-flow siphon-priming works well only in limited applications; PA1 (e) Pumping or pouring to fill a siphon demands extra steps for too-small advantage; PA1 (f) A conventional vacuum-pump is inefficient for siphon-priming. A vacuum pump good for efficient siphon startup-priming is overpowerful for maintaining prime in an operating siphon; and a vacuum pump that can maintain prime efficiently is underpowered for startup. Either way, when the siphon is filled, a need to prevent liquid entry to the pump is an unwelcome complexity; PA1 (g) Siphon-priming by utilizing subatmospheric inlet pressure ("suction-lift") of liquid handling pumps is theoretically possible, but no practical prior examples have been found; PA1 (h) Venturi-effect siphon-priming uses a small fraction of pump-outflow power to produce only enough vacuum to fill low elevation siphons; PA1 (i) High-elevation, high-volume and long-extension siphons have seldom been attempted, largely due to the limitations of available priming methods; PA1 (j) After a siphon is primed by any method that does not continue during operation, gases in the siphon accumulate at the top. When the liquid level drops to a predetermined level the flow stops, re-priming is necessary before flow can resume; and PA1 (k) For lack of reliable and efficient siphon-priming, few if any pipelines use siphons. Most pipeline flow is forced through by pumps consuming energy from non-renewable resources. PA1 (a) To provide a simple and effective hydraulic vacuum pump (HVP) that requires no valves and only one mechanical moving part, the pump impeller; PA1 (b) To provide a new and improved way of starting siphon flow by simply starting the hydraulic vacuum pump (HVP), which causes siphons to prime and remain primed to transport water by the power of gravity continuously with no further operator action; PA1 (c) To provide a HVP that can serve to prime and maintain prime equally well in siphons that transport or recirculate liquid; PA1 (d) To provide a HVP which, when used to maintain prime in elevated-siphon segments of a high-volume, long-distance fluid transport pipeline, would enable pipeline fluid flow by gravity power in place of pumps that consume energy from non-renewable resources. Power consumed for startup vacuum-priming and HVP priming maintenance to enable gravity-powered siphon flow, would be a small fraction of power consumed by pump-powered flow. Also, minor leaks in the miles of elevated-siphon-sections of a pipeline would not lose contents or contaminate environment; but air would leak in and signal the problem, and contents would not leak out; PA1 (e) To provide a HVP that can prime as many kinds of siphons as possible, including single or multiple legs, high or low volume, long or short extension, high or low elevation, and single or multiple elevations of single or multiple interconnected siphons; PA1 (f) To provide a HVP that will work with any kind of pump that has subatmospheric inlet pressure and will not trap gases or be damaged by mixtures of liquids and gases; PA1 (g) To provide a new kind of vacuum pump that will continuously and reliably extract gases mixed with or entrained in liquids, from siphons or other space to be vacuumed; PA1 (h) To provide a HVP that is adaptable to work with many different combinations of liquids and gases; PA1 (i) To provide a HVP in which the speed and siphon-elevation limits of priming action may be primarily controlled by adjusting the pump-priming inlet orifice size; and PA1 (j) To provide a HVP that assures such reliable and convenient siphon operation that siphons with gravity-powered flow can replace energy-consuming pump-powered flow in many new uses that will each result in savings of non-renewable energy resources.
In all of the prior art found, there is a clear and consistent need for a more simple, reliable, controllable and versatile siphon-priming method.